1. Field of the Invention
The present invention concerns a method and a device for data transmission between two components moving relative to one another, in particular between the rotating part and the stationary part of a computed tomography apparatus, of the type wherein the first component has a number of transmission segments arranged along a movement direction and the second component has a number of receiver units arranged along the movement direction, the spacing of which is less than or equal to a center distance of the transmission segments and wherein the data are divided for parallel transfer to a number of the transmission segments, and each receiver unit receives data only from the transmission unit in whose immediate proximity it is directly located.
2. Description of the Prior Art
In imaging medical technology (a primary application field of the present invention), computed tomography systems are frequently used in which a very large number of measurement data are acquired in a short time, and are transmitted to an image reconstruction unit and further processed therein to reconstruct the desired images. The data transmission system required for this purpose must enable a high speed transfer (due to the large number of measurement data accumulating per time unit) and must also ensure an optimally disruption-free transmission between the rotating part and the stationary part of the computed tomography system. The techniques of capacitive coupling as well as optical coupling that can also be used in the present method and the present device, are the primarily used techniques for the data transfer between the rotating part and the stationary part.
For example, U.S. Pat. No. 5,140,696 A describes a device for signal transmission between two components moving relative to one another, in particular in a computer tomograph in which a circular strip conductor is arranged as a transmitter at the periphery of the rotating part of the gantry and a short segment of a strip conductor is arranged as a receiver antenna at the stationary part of the gantry in immediate-proximity to the transmitter conductor. With this capacitive coupling technique the data are modulated on a carrier signal and injected into the circular strip conductor. A portion of the signal energy of the electromagnetic signal propagating in the strip conductor can be detected by the receiver antenna at the stationary part as a result of the radiated energy that is present in the intervening space between the two parts rotating counter to one another. After demodulation, the data are then available at the stationary part. However, with the increasing data rate of modern computed tomography systems (in particular multi-line systems) the transmission capacity of a single pair (composed of strip conductor and receiver antenna) is no longer sufficient, such that at least two such pairs must be arranged next to one another in order to be able to transfer the accumulating data in real time. This increases the costs of the transfer system, requires additional structural space at the rotating part and increases its weight.
To increase the transmission capacity, U.S. Pat. No. 6,327,327 teaches subdividing the circular rotary strip conductor into a number of segments that are separated from one another and to provide a corresponding number of receiver antennas at the side of the stationary part. The data to be transmitted can then be divided among the multiple transmission segments and can be transmitted in parallel between the transmitter segments and the receiver antennas. Each transmitter segment is thereby connected with its own transmitter that respectively transmits a subset of the accumulating data to the currently opposite receiver antenna. The transmission capacity of the data transmission system is increased by this provision of a number of parallel transmission channels. With this technique, however, transmission problems regularly occur when a receiver antenna moves directly over the gap between two adjacent transmission segments. In this time span the antenna receives data from two transmission segments since, for a sufficient reception quality, it cannot be executed arbitrarily short. Given an arrangement with N transmission segments this problem occurs N times during a complete rotation of the gantry. The respective time span of such an interruption depends primarily on the length of the receiver antenna as well as the rotation speed of the gantry. For low data rates of, for example, 60 Mbps the bit length in the micro-strip conductor is 333 cm and the required length of the receiver antenna is 25 cm in order to achieve a sufficient transmission quality. The large length of the receiver antenna is based on the decreasing coupling capacity for the low-frequency transmission components. At higher data rates the antenna can be executed shorter. Given a data rate of, for example, 2500 Mbps the bit length in the micro-strip conductor is 8 cm and the required length of the receiver antenna is 4.3 cm, such that shorter interruption time spans result. The amount of data that is lost in the interruption time spans also simultaneously increases given a higher data rate.
To solve this problem, in U.S. Pat. No. 6,327,327 it is proposed to use two parallel arrangements composed of an annular, segmented strip conductor and receiver antenna whose transmitter segments are offset counter to one another in the circumferential direction. The data reception is then respectively switched between the two arrangements when the receiver antennas are respectively directly located between two transmitter segments in an arrangement. The arrangement of two parallel arrangements again increases the costs, requires additional structural space at the rotating part and increases its weight.
Furthermore, for reconstruction of the data received via the receiver antennas as well as for switching between the arrangements, an angle transmitter is required in the arrangement of U.S. Pat. No. 6,327,327, from whose signals the current position of the transmission segments relative to the receiver antennas can be derived. This information required in the receiver device in order, among other things, to be able to assemble the segments of the serial bit stream received by the different receiver antennas in the correct order.